GB2230312A - Flowline connection system - Google Patents

Abstract

A method and apparatus for remote flowline connection, particularly suited to deep water multi-well installations comprises the use of a manifold skid (22) for skidding or sliding alignment of flowline connectors (26), thereby avoiding the flexible flowline loops which conventionally accommodate the connector swallow. <IMAGE>

Description

FLOWLINE CONNECTION SYSTEN i The present invention relates to a flow line connection system of a type which is suitable for use with subsea installations which are used to recover oil or gas.

In the equipment which produces oil and gas from subsea installations, it is necessary to make and break connections in the flowlines, the conduits which transport fluid from (and to) the subsea wells. These connections must be leak-free, often at elevated working pressure (5000 psi +).

The need for making and breaking these flowline connections arises both at the installation of the subsea equipment, and on those occasions when one or more components in the flow stream must be retrieved for repair or replacement.

In shallow water depths the connection of flowlines can be accomplished or assisted by divers. As water depth increases beyond the safe limit for effective diving, the connections must be automatic, or "diverless".

The flow stream arising out of the well is ordinarily vertical (upward) and the flow stream in the subsea flowline or pipeline is ordinarily horizontal (along the seabed). The elevation at which the flow exits the well's controlling valves (christmas tree) is generally higher than the elevation of the flowline on the seabed. Because of this, the flowstream will generally be turned from the vertical to the horizontal and back one or more times between the tree and the flowline on the seabed. Similarly, the connection(s) in the flowline may be vertical or horizontal (or both).

As the foregoing suggests, the basic components of the flow stream are the tree and the subsea flowline. There may also be other retrievable components besides the tree. These components might include specialized piping spools, whose interchange will re-route the flow in some desirable way. They might include a distribution manifold, a valve package which allows remote switching of flow paths. The presence of these added components will add turns in the flow stream and will add connections.

A remote, diverless flowline connection must enable the mating ends to be located and oriented relative to one another in space and enable the ends to be displaced or moved together to mate, seal and lock.

Locating and orientating is a problem because of the inexact nature of the installation of the components on the seabed. This is especially true of the wellhead (and associated tree) and of the subsea flowline.

Furthermore, a multitude of both machining and fabrication tolerances enter into the final position of the system elements.

Moving the mating ends together is a problem because the elements of the system are not naturally mobile.

Besides the problem of the great weight and bulk of the components of the system, the two major elements, the tree and the subsea flowline, are essentially fixed rigidly in space.

Locating and orienting is generally accomplished by use of added care at installation, and by use of carefully constructed and fitted guide structures.

Moving the mating ends together is generally accomplished in two steps.

First, the flowline, which has some limited flexibility or mobility, is deflected into a known position (a) the anchor point of the "pull-in" method, or (b) the pivot point of the "lay-away" method. Apparatus for achieving the pull-in and lay-away methods is depicted in figures 1 and 2, respectively, of the accompanying drawings.

Second, the final mating is accomplished by a combination of translation and flexure of the component segments of the flowline. It is this final step which defines the critical technology, the success or failure, of the chosen method.

The final translation consists of two parts, that required to take-up the last bit of fit and aligment, and that required to accommodate the engagement ("stab-in") of the chosen end connector. Similarly, the flexure consists of two parts, that required for the 1st bit or fit and alignment, and that required to accommodate the "stab-in" translation.

In a vertical connection the final translation is provided by the lowering and landing of a component assembly (the tree) upon the upturned end of the mating vertical flowline end. The flexure to complete alignment is motivated by the considerable weight of the landing assembly, directed through guide sleeves, cones, or the like.

In a horizontal connection, the final translation is provided by a push-pull hydraulic ram, which forces the ends together. Typical travel is 12" - 18". The flexure which permits this movement in these otherwise rigid pipes is provided by incorporating large "expansion loops" in the flowline, generally on the assembly other than the sled. Typical expansion loops are depicted by reference numeral 12 in figures lb, 2a and 2b.

The piping attached to these end connections is deflectedfor the translation distance. Typically this distance is quite large, necessitating the special design involves increasing the piping lenght to reduce its unit deflection ratio. This extra lenght is generally coiled to form expansion loops.

It is an object of the present invention to facilitate the manufacture and installation of flowline connections, particularly but not exclusively within a multi-well template. This is achieved by mounting the flowline connector on a skid which is capable of orienting and landing in a well base structure with subsequent horizontal translation of the skid to the flowline connection position. The invention can thus eliminate the need for the conventional flexible pipe loops used to accommodate the connector swallow".

Preferably, the skid carries the tree flowline mandrels, all common piping systems and the completion control system. Horizontal translation of the skid can thus simultaneously engage the flowline connector, align the tree flowline mandrels to their correct position and lock the skid to the well base structure or template. The controlled engagement and release of the flowline connection obtainable with use of the present invention is particularly beneficial.

In addition, elimination of additional pipework in the form of expansion loops provides considerable cost savings.

An embodiment of the invention will now be described in detail, by way of example only and with reference to the accompanying drawings, in which : Figures la and lb illustrate the known "pull-up" method of achieving flowline connection, Figures 2a and 2b illustrate the known "lay-away" method of achieving flowline connection, Figure 3 is a block diagram indicating components carried by each part of a system which embodies the present invention, Figure 4 is a partial schematic section of the skid of the system of figure 3, Figure 5 is a simplified and exploded perspective view of the skid of the system of figure 3, and Figure 6 is a perspective view showing the sled of figures 4 and 5 in engagement with a multi-well template structure.

The subsea guide structure illustrated in figures 3-6 is an intergrated multi-well template. This can be preferable to the use of individual satellite wells because it offers reduced cost in the subsea flowlines; only one test flowline is required instead of two (or three). This template approach also reduces the complexity and cost of the subsea controls, requiring just one large pod and subsea umbilical, instead of two (or three).

The diverless flowline connection system uses, in part, conventional technology pull-in technology, as has been used extensively. The flowline system is designed to permit full access to the system components for retrieval or repair during the critical installation and test period. The invention permits elimination of the bulky, costly expansion loops ordinarily found in this type of horizontal system.

The flowline connections to the sled are intended to be fixed and not disturbed once successful connection is made. For these connections a horizontal connector is preferred. This is the more typical method of making such connections, but requires controlled manipulation of the flowlines; here, the manipulation is required only once.

The flowline connections to the trees, on the other hand, are designed to be readily disconnected in the event that tree or well servicing is required. For this reason vertical connectors are preferred. Here, no manipulation of the flowlines is required, since the mating of the connectors is accomplished with the landing motion of the tree.

The template mounted production manifold permits use of a single test/service flowline to serve both wells.

This retrievable unit thus reduces overall system cost while maximizing platform access to the well bores.

Use of individual production flowlines for each well has been chosen in this embodiment, over "co-mingling" the flows in a single, larger flowline. Co-mingling could however be used.

For the subsea production system illustrated in figure 3, two different flowline connections are required. The sled 20 connects to the manifold skid 22 through a horizontal connection 26, involving a pull-in of the sled 20 and a lateral movement of the manifold skid 22.

The tree 24 connects to the manifold skid 22 by a vertical connection 28.

The system includes; - the template's sled receiver 30, including a ramp 32 and guides 34 - the sled assembly 20 - the pull-in tool (not shown) - the manifold skid assembly 22 The template 18 is provided with a dedicated sled receiver "porch" 30 to receive the flowline sled 20. A ramp 32 and lateral guides 34 are included, to assist in the remote positioning of the sled 20 as it pulls and locks in. Just inboard of the porch 30 is a remote connector mandral 40, fixed to the template structure.

This provides the anchoring point for the pull-in tool and later for the hydraulic skidding cylinder 42 on the manifold skid 22.

It is in theory possible to perform the sled pull-in before the template wells 16 are drilled and completed.

However, this is not recommended, as it places the critical sled at risk of damage during subsequent operations. Also, although the pull-in loads are not expected to exceed 50-100 kips, the template 18 will bear the pull-in loads better if the wells 16 are in place.

Thus, it is desirable that the pull-in be performed after all drilling, and preferably after all completion operations.

The flowline laying operation concludes with the flowlines 14 being connected to the sled 28 and laid back on the seabed, complete with towing cable and locator beacon. The sled 20 at that time will have been fitted with a circulation cap on the hub. This cap will allow the remote circulating and pressure testing of the lines. It is removed (ROV operation) after the sled 20 is locked to the template 18 and before the manifold skid 22 is run.

The pull-in operation begins when an ROV attaches a lifting pendant line to the free end of the towing cable and passes that line to the semi-submersible drilling vessel (SSDV) which will accomplish the pull-in. At the same time the ROV inspects the sled 20 and confirms its location and heading. The lifting line and the towing cable are recovered to the SSDV.

The towing cable is passed through the pull-in tool and over its sheave. The pull-in tool is run on drill pipe and two light guide arms, and the towing cable is redeployed at the same time and at the same pace. The utility umbilical is deployed with the tool. The tool lands on and locks to the anchor hub 40 on the template 18.

The sled 20 is pulled back into the template 18 by pulling the towing cable back to the SSDV. The final seating of the sled 20 in receiver structure 30 is viewed on subsea T.V., or by the ROV. When the sled 20 is fully seated, the tool deploys its hydraulically extended lock pin, which fixes the connection of the sled 20 to the template 18.

The seating of the lock pin automatically releases the towing cable, allowing the tool and cable to be recovered to the SSDV. It is still possible at this point in the operation to recover the sled 20, if required by some unforseen circumstance. The lock pin can be pulled using a lifting line deployed from the SSDV. This operation would require an ROV.

Anticipated pull-in loads of 50-100 kips can be confirmed by prior onshore testing. Also, onshore testing can be used to determine if the towing cable will provide sufficient load to align the sled 20 to the template receiver 30. If there is any doubt, two hydraulic jacks can be fitted between the template 18 and the sled 20 to increase the aligning moment.

Finally, onshore testing can be used to confirm that the sled 20 can be pulled in from any point in the projected "target area", into which the sled 20 will initially be placed.

With the sled 20 locked to the template 18 and the pull-in tool recovered, an ROV is deployed to unlock the circulating cap from the sled hub, and to attach the rig's lifting line to allow its recovery. This step should be delayed if the manifold skid 22 is not ready to be deployed.

The manifold skid assembly 22 is the next item to be installed. Assembly 22 is illustrated in figures 4 and 5. It consists of three basic elements, the lower assembly 44, the upper skid assembly 46, and the recoverable manifold assembly 48. The upper and lower assemblies 44, 46 are not independently recoverable, the manifold 48 is.

The lower assembly 44 consists of two parallel guide rails 50, a latch-type connector 52, and two guide sleeves, all disposed in a fixed, rigid relationship to one another. The guide sleeves receive two guide lines from the front-center two guide posts on the template 18, and provide installation guidance for the manifold skid assembly 22. The connector 52 latches to the anchor hub 40, and provides both the initial latching of the skid 22 to the template 18 and the reaction point for the skidding effort. The two skid rails 50 provide a slidable connection between the upper and lower assemblies 44, 46. Downward facing pins 54 on the rails 50 engage locator holes in the template 18.

Skid feet 56 on the upper assembly 46 slidably engage the rails 50 of the lower assembly 44. In addition, the hydraulic skidding ram 42 is trunnion-mounted to the upper assembly 46 and pinned to the latch connector 52 of the lower assembly 44.

The upper skid assembly 46 is a rigid structure slidably fixed to the lower assembly 44. It consists of a flat skid structure 58 (figure 5) with an 18 3/4" wellhead-style mandrel 60 at its center (resembling a BOP test stump skid). The central hub is fitted with a remotely retrievable manifold block valve assembly 62, based on an 18 3/4" wellhead type connector. Hydraulic control stab rings 64 communicate control fluid from the manifold running tool (subsea tree running tool) to the skidding ram 42 and to the forward, horizontal flowline sled connector 66. A function is also piped to permit pressure testing of the connection to the sled 20.

The two 4" x 2" concentric vertical flowline connector hubs 68 are carried on the sled 22, hard-piped back to the central manifold hub 60. This hub 60 in its turn is hard piped to the forward facing horizontal flowline sled connector 66.

The subsea control pod 70 and ROV interface pod 72 (Figure 6) are mounted at the rear of the upper skid assembly 22. These are hard piped to the control stab rings on the vertical flowline connectors, on the horizontal flowline sled connector 66, and on the manifold connector 60.

The manifold skid assembly 22 is run on the tree running tool (the lower riser package is omitted and only the emergency disconnect package is used). When the manifold skid 22 is landed and latched to the template 18, the skidding ram 42 is hydraulically retracted, shifting the upper assembly 46 forward to mate its flowline connector 66 with the hub 34 on the sled 20.

The forward motion of the skid assembly 22 simultaneously acts to lock the whole manifold skid assembly 22 to the template 18. A skid retention lock 38 is provided.

Once the manifold skid 22 is landed, the connector 66 is skidded, locked and tested, the running string is retrived. Debris caps on the 4" x 2" concentric hubs 68 remain to be retrieved before running the trees 24.

The manifold skid 22 provides the connection between the flowlines 14 on the sled 20 and the flowlines on the trees 24. It incorporates the female horizontal connector 66 (to lock to the sled), the removable manifold assembly 62, and the male vertical connector hubs 68 (to lock to the trees 24).

The manifold skid 22 also provides the connection between the control umbilical on the sled 20 and the functions on the trees 24. It incorporates the female horizontal control stab (to lock to the sled), the recoverable subsea pod (with ROV override pod), and the male vertical control stabs (to lock to the trees). All control lines run from the sled connection to the pod, then back to the lower, male control stab rings on the connectors; the chemical injection lines run directly from the sled connection to the stab rings at the tree (bypassing the pod).

Because the upper and lower assemblies 44, 46 of the manifold sled 22 can skid laterally relative to one another, no expansion loops" are required in the flowlines to accommodate the horizontal translation that is used to link to the sled 20. This saves space and weight.

Because the "fixed" skid rails 50 are included in the lower assembly 44, they are not subject to damage during the drilling operation, as they would be if left as a component of the template 18. Also, this approach allows pre-assembly (on deck) and testing of the skidding ram 42.

The manifold skid 22 is run with the emergency disconnect connector of the tree running tool, and with the associated stress joint and drill pipe running string. The control system is the same as used with the running/workover of the trees, but the only active functions are the manifold connector (lock/unlock), sled connector (lock/unlock), and the skidding ram (retract/extend).

The manifold skid 22 is landed in a template bay between the wellhead bays. It is installed after all drilling and after the flowline sled 20 is pulled in and locked.

An embodiment of the invention has been described in detail. However, it will be apparent to those skilled in the art from the description of this embodiment that various modifications can be made without departing from the scope of the invention. All such modifications are intended to be covered by the appended claims.

Claims (21)

Claims:

1. A flowline connection system comprising a skid assembly carrying at least one mandrel for connection to a well system and a flowline connector, the assembly having an upper sub-assembly and a lower sub-assembly, the sub-assemblies providing for relative motion therebetween so as to enable mating alignment of the flowline connector.

2. A flowline connection system as claimed in claim 1, wherein the skid assembly carries a recoverable manifold.

3. A flowline connection system as claimed in claim 1, wherein the skid assembly includes a hydraulic ram operable to generate the said relative movement between the sub-assemblies.

4. A flowline connection system as claimed in claim 1, wherein a skid retention lock is provided between the sub-assemblies, the lock being operable to prevent further relative motion between the sub-assemblies once the said mating alignment has been establihed.

5. A flowline connection system comprising a sub-sea structure, a sled and a skid, the sled and skid carrying complementary sections of a flowline connector, the sub-sea structure having a section for receiving and retaining the sled and skid with the skid having two sub-assemblies with the capability of relative motion therebetween so as to enable mating alignment of the flowline connector sections when the sled and skid are retained on the sub-sea structure.

6. A flowline connection system as claimed in claim 5, wherein the sub-sea structure is a multi-well template.

7. A flowline connection system as claimed in claim 5, wherein the skid assembly carries a recoverable manifold.

8. A flowline connection system as claimed in claim 5, wherein the skid assembly includes a hydraulic ram operable to generate the said relative movement between the sub-assemblies.

9. A flowline connection system as claimed in claim 5, wherein a skid retention lock is provided between the sub-assemblies, the lock being operable to prevent further relative motion between the sub-assemblies once the said mating alignment has been establihed.

10. A flowline connection system as claimed in claim 5, wherein the upper of the skid sub-assemblies is provided with at least one christmas tree flowline mandrel rigidly connected to the flowline connector section carried by the skid.

11. A flowline connection system as claimed in claim 10, wherein with the relative motion between the sub-assemblies being horizontal the christmas tree flowline mandrel is substantially vertical.

12. A flowline connection system as claimed in claim 5, wherein the sub-assemblies are slidably interconnected by parallel rails.

13. A flowline connection system as claimed in claim 5, wherein the receiving section of the sub-sea structure comprises a ramp and lateral guides.

14. A flowline connection system as claimed in claim 5, wherein the skid carries a control system coupler and a remotely operated vehicle interface.

15. A flowline connection system as claimed in claim 11, wherein the sub-sea structure is a template having a portion defining a wellhead space and retaining a wellhead therein, the receiving section for the sled and skid being adjacent the wellhead space with the christmas tree flowline connector being received in the wellhead space.

16. A flowline connection system as claimed in claim 10, wherein the christmas tree flowline mandrel is connected to the flowline connector section carried by the skid via a production manifold mandrel.

17. A flowline connection system as claimed in claim 15, wherein the wellhead space defining portion of the template is provided with means for guiding a production tree into contact with the wellhead and tree flowline mandrel so as to establsh fluid contact therebetween.

18. A flowline connection system as claimed in claim 15, wherein the template is a two well template having two wellhead space defining portions with the receiving section for the sled and skid being provided therebetween.

19. A method of remote connection of a flowline to a well system comprising the steps of: providing a sled carrying a flowline connector attached to the flowline, providing a skid carrying a flowline connector and a well system connector, the skid having two sub-assemblies with the capability of relative motion therebetween, providing a structure in the well system for receiving and retaining the sled and skid, pull-in of the sled to the structure, landing the skid on the structure, and effecting relative motion between the sub-assemblies of the skid so as to cause mating alignment of the said flowline connectors and alignment of the well system connector.

20. A flowline connection system substantially as herein before described with reference to and as illustrated in figures 3 to 6 of the accompanying drawings.

21. A method of remote connection of a flowline to a well system substantially as herein before described with reference to and as illustrated in figures 3 to 6 of the accompanying drawings.